fflush.c

/* fflush.c -- allow flushing input streams Copyright (C) 2007 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. *//* Written by Eric Blake. */#include <config.h>/* Specification. */#include <stdio.h>#include <errno.h>#include <unistd.h>#include "freading.h"#include "fpurge.h"#undef fflush/* Flush all pending data on STREAM according to POSIX rules. Both output and seekable input streams are supported. */int
rpl_fflush (FILE *stream)
{
int result;
off_t pos;
/* When stream is NULL, POSIX and C99 only require flushing of "output streams and update streams in which the most recent operation was not input", and all implementations do this. When stream is "an output stream or an update stream in which the most recent operation was not input", POSIX and C99 requires that fflush writes out any buffered data, and all implementations do this. When stream is, however, an input stream or an update stream in which the most recent operation was input, C99 specifies nothing, and POSIX only specifies behavior if the stream is seekable. mingw, in particular, drops the input buffer, leaving the file descriptor positioned at the end of the input buffer. I.e. ftell (stream) is lost. We don't want to call the implementation's fflush in this case. We test ! freading (stream) here, rather than fwriting (stream), because what we need to know is whether the stream holds a "read buffer", and on mingw this is indicated by _IOREAD, regardless of _IOWRT. */if (stream == NULL || ! freading (stream))
return fflush (stream);
/* POSIX does not specify fflush behavior for non-seekable input streams. Some implementations purge unread data, some return EBADF, some do nothing. */
pos = ftello (stream);
if (pos == -1)
{
errno = EBADF;
return EOF;
}
/* To get here, we must be flushing a seekable input stream, so the semantics of fpurge are now appropriate to clear the buffer. To avoid losing data, the lseek is also necessary. */
result = fpurge (stream);
if (result != 0)
return result;
#if defined __sferror && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
{
/* Disable seek optimization for the next fseeko call. This tells the following fseeko call to seek to the desired position directly, rather than to seek to a block-aligned boundary. */int saved_flags = stream->_flags & (__SOPT | __SNPT);
stream->_flags = (stream->_flags & ~__SOPT) | __SNPT;
result = fseeko (stream, pos, SEEK_SET);
stream->_flags = (stream->_flags & ~(__SOPT | __SNPT)) | saved_flags;
}
return result;
#else
pos = lseek (fileno (stream), pos, SEEK_SET);
if (pos == -1)
return EOF;
/* After a successful lseek, update the file descriptor's position cache in the stream. */# if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
stream->_offset = pos;
stream->_flags |= __SOFF;
# endifreturn 0;
#endif}